Leland Stanford Junior University

Mihir Pendse

Brian Rutt

Obtaining minimum duration parallel transmit pulses for simultaneous multislice imaging that includes minimizing specific absorption rate hotspots, using an IMPULSE pTx optimization method to determine multiple spoke locations and multiple channel weights for multiple slices while enforcing a specified flip angle inhomogeneity tolerance over the multiple slices when excited, applying a control algorithm to conform a simultaneous multislice (SMS) pulse to the excited multiple slices to minimize a cost function having terms corresponding to an excitation accuracy and a pulse power, where a regularization term in the cost function is configured by the control algorithm for excitation accuracy while limiting a peak pulse power, and applying a time-optimal variable rate selective excitation (VERSE) to enforce a peak power constraint with a minimum pulse duration by reshaping a RF waveform and a gradient waveform without altering an excitation profile if the peak power limit on a channel is exceeded.

Methods for mitigating local SAR hotspots and flip angle uniformity in ultra-high field simultaneous multislice imaging using parallel transmission

A method for providing SAR focusing at a target in a body using an MRI system is provided. A computed pulse is provided at a lower power to the body. A MR thermometry is performed. A map is created from the MR thermometry to determine if a hotspot aligns with the target. If the target does not align with the hotspot, then the steps are performed comprising, recomputing the computed pulse, providing the computed pulse at a lower power to the body, performing MR thermometry, creating a map from the MR thermometry to determine if a hotspot aligns with the target, and repeating these steps until the hotspot aligns with the target. The computed pulse is applied at a higher power to the body to provide the desired SAR at the target. Temperature change is monitored with MR thermometry the previous two steps are repeated until desired temperature is achieved.

Method and apparatus for SAR focusing with an array of RF transmitters

A method for providing an image of a subject in a magnetic resonance imaging MRI system with parallel transmission (pTx) is provided. A localizer scan of the subject is provided. Body anatomy is determined from the localizer scan. The body anatomy is matched with at least one body model of a plurality of body models. Band Bmaps are calculated from the body anatomy. The electric fields from the at least one body model and constraints are used to simultaneously determine a plurality of excitation pulses for a pTx. MRI is performed on the subject using the determined excitation pulses. Global SAR is monitored in real time to ensure all time-averaged constraints are satisfied simultaneously.

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Fremont, CA, United States of America

Mihir Pendse